It is well understood that certain compounds and nutrients contained within packages can be negatively impacted by exposure to light. Many different chemical and physical changes can result to molecular species as either a direct or indirect result of exposure to light, which can collectively be defined as photochemical processes. As described in Atkins, photochemical processes can include primary absorption, physical processes (e.g., fluorescence, collision-induced emission, stimulated emission, intersystem crossing, phosphorescence, internal conversion, singlet electronic energy transfer, energy pooling, triplet electronic energy transfer, triplet-triplet absorption), ionization (e.g., Penning ionization, dissociative ionization, collisional ionization, associative ionization), or chemical processes (e.g., disassociation or degradation, addition or insertion, abstraction or fragmentation, isomerization, dissociative excitation) (Atkins, P. W.; Table 26.1 Photochemical Processes. Physical Chemistry, 5th Edition; Freeman: New York, 1994; 908). As one example, light can cause excitation of photosensitizer species (e.g., riboflavin in dairy food products) that can then subsequently react with other species present (e.g., oxygen, lipids) to induce changes, including degradation of valuable products (e.g., nutrients in food products) and evolution of species that can adjust the quality of the product (e.g., off-odors in food products).
As such, there is an art-recognized need to provide packaging with sufficient photoprotective properties to allow the protection of the package content(s). In certain studies, actual packaging systems and photochemical reactors have been used as a means to provide an indication of photoprotective performance of packaging concepts. However, generally these studies allow for the evaluation of only a single packaging concept and do not demonstrate sufficiently robust methods to allow for relative comparisons between experiments, nor the capability to produce performance design models based on the results.
For instance, the work of Kline et al. (Kline, M. A.; Duncan, S. E.; Bianchi, L. M.; Eigel, W. N., III; O'Keefe, S. F.; Light Wavelength Effects on a Lutein-Fortified Model Colloidal Beverage. J. Agric. Food Chem. 2011, 59, 7203-7210) studying the light effects on a model colloidal beverage acknowledges the challenge to make relative comparisons between experimental conditions with their method due to changes in light intensity; however, they fail to demonstrate a suitable solution. Similarly, Webster et al. (Webster, J. B.; Duncan, S. E.; Marcy, J. E.; O'Keefe, S. F.; Effect of narrow wavelength bands of light on the production of volatile and aroma-active compounds in ultra high temperature treated milk. Int. Dairy Journal. 2011, 21, 305-311), studying the effects of light on milk, acknowledge the inability to make direct comparisons between all experiments due to differences in light energy output as a limitation of their capability (see also Webster, J. B.; Duncan, S. E.; Marcy, J. E.; O'Keefe, S. F.; Controlling Light Oxidation Flavor in Milk by Blocking Riboflavin Excitation Wavelengths by Interference. J. Food Sci. 2009, 74, S390-S398). As another example, in a study by Palanuk (Palanuk, S. L.; Warthesen, J. J.; Smith, D. E.; Effect of agitation, sampling location and protective films on light-induced riboflavin loss in skim milk. J. Food Sci. 1988, 53, 436-438), sampling location was shown to influence the results in studies of the effects of light on riboflavin in skim milk.
Additionally, studies in this field frequently require an extended testing period, such as days or weeks. For instance, Cladman (Cladman, W.; Scheffer, S.; Goodrich, N.; Griffiths, M. W.; Shelf-life of Milk Packaged in Plastic Containers With and Without Treatment to Reduce Light Transmission. Int. Dairy Journal. 1998, 8, 629-636) performed a study on photoprotective properties of materials that required a twenty day period to expose the samples. As another example, while Saffert et al. report two studies (Saffert, A.; Pieper, G.; Jetten, J.; Effect of Package Light Transmittance on the Vitamin Content of Pasteurized Whole Milk. Packag. Technol. Sci. 2006, 19, 211-218; Saffert, A.; Pieper, G.; Jetten, J.; Effect of Package Light Transmittance on Vitamin Content of Milk. Part 2: UHT Whole Milk. Packag. Technol. Sci. 2008, 21, 47-55) that explore package performance related to retaining nutrients in milk, they conducted the study under conditions that required days of exposure.
Given the above, a robust scientific method to rapidly quantify photoprotective performance of packaging concepts in a way that allows relative comparisons between the packaging concepts and is relevant to the conditions used for such packaging concepts in their targeted real-world applications is needed. These methods are needed to allow for the creation of performance design models for packaging concepts, and to allow for efficient design of photoprotective packages that achieve the required balance of performance attributes for a given package cost, weight, material usage, or other design requirements.